In the related art, there is provided a vehicle equipped with a suspension that includes air springs using compressed air and the like. There is also a vehicle equipped with a vehicle height adjustment apparatus using the air springs. There is a so-called closed type vehicle height adjustment apparatus. This type of vehicle height adjustment apparatus increases a vehicle height by supplying a working fluid (high-pressure air) stored in a pressure tank to the air springs that change a suspension state of each wheel. The vehicle height adjustment apparatus may pressure-feed the working fluid to the air springs using a compressor. In contrast, the compressor may draw the working fluid from the air springs to the pressure tank so as to decrease the vehicle height. In this vehicle height adjustment apparatus, a group of valves are interposed between the pressure tank and the compressor, and the air springs so as to select the flow direction of the working fluid. JP 2002-337531A is an example of the related art.
In the above-mentioned closed type vehicle height adjustment apparatus, a pressure difference between the forward and rearward pressure tubes of the pressure tank and the compressor may increase after the drive of the compressor. For this reason, pressure may be unintentionally applied to the group of valves that are interposed between the pressure tank and the compressor, and the air springs. It is desirable to reduce the impact of the unintended pressure so that the valves can be smoothly controlled, that is, the vehicle height adjustment apparatus can be smoothly controlled.